I’d want 100Ah minimum myself, actually more. But in your case.
I’d buy a Walmart marine flooded deep cycle and leave it outside- no off gas concern. One 100Ah lead battery is ~<=50Ah useable.
One marine deep cycle lead acid battery at 100Ah nominal needs 200-300W of panels, 200W minimum at your latitude. 400W in series might still be marginal in winter.